Hitherto, economization of air-conditioning expenses by preventing elevation of the internal temperature in the inside of structures by direct sun light, inhibition of vapourization and reduction of volatile components in the inside of tankers, natural gas-conveying ships and land tanks by coating the outer surfaces of such structures, and improvement of the freezing effect of tanks and household electric appliances have been strongly desired. For instance, reduction of crude oils because of vapourization of the volatile contents from tankers is noticeable, and it is said that the vapourization loss is to be from 0.2 to 0.5 % of the total loadage per one shipping from the Middle and Near East to Japan.
In order to overcome the problem, a white pigment such as titanium oxide, or a colored pigment, has hitherto been used as a solar heat-shielding paint composition. While the solar heat-shielding effect is somewhat effective in the case of a white pigment, the solar heat-shielding effect is extremely lowered in the case of a colored, but not white, pigment. Accordingly, development of a paint composition which may have a high solar heat-shielding effect even when colored in any desired color has been requested.
On the other hand, an aluminium paint composition containing a flaky aluminium powder is also already been known as a solar heat-shielding paint composition for roofs of structures or outer surfaces of tanks. However, the color of such aluminium paint composition is also limited and the composition is insufficient in the point of the durability. In addition, the abrasion resistance of the resulting paint is poor and therefore the composition has another problem that it is unsuitable to the place where persons will walk thereon.
Under the circumstances, a heat-reflecting enamel containing antimony trioxide, antimony dichromate or an alkali metal dichromate has been proposed for the purpose of overcoming the problems (Japanese Patent Application Laid-Open No. 56-109257), which is, however, unfavorable from the viewpoint of environmental sanitation as it contains a heavy metal. In addition, a sufficient effect could not be attained by such enamel coating.
An emulsion-coating composition containing fine glass beads having a grain size of from 20 to 350 .mu.m, a coating composition containing white pigment-containing synthetic silica grains having a grain size of 300 .mu.m or less, and a method of forming a metal plate coated with a coating composition containing fine glass beads having a grain size of from 5 to 300 .mu.m have also be proposed (Japanese Patent Publication No. 55-33828, Japanese Patent Application Laid-Open No. 55-120669, Japanese Patent Application Laid-Open No. 55-74862). However, though these have an excellent solar heat-shielding effect, the coated surface has a rough pattern and has a poor pollution-resistance and the solar heat-shielding effect of the coated surface becomes problematically because it becomes extremely lower, with the lapse of time. By such means, therefore, it is difficult to obtain a coating composition or a coated structure which can be colored in any desired color and which may maintain an excellent solar heat-shielding effect for a long period of time.
Combined use of an organic material such as CoCr.sub.2 O.sub.7, K.sub.2 SO.sub.4, SiN.sub.4, K.sub.2 SO.sub.3, SiO.sub.2, Al.sub.2 SiO.sub.5 or the like or an organic material such as vinyl fluoride/vinylidene fluorice copolymer, polyoxypropylene, polypropylene, difluoride copolymer, vinylidene difluoride, polyethylene chloride trifluoride, polyethylene tetrafluoride or the like and rutile titanium oxide has also been proposed (Japanese Patent Application Laid-Open No. 60-86173). However, the inorgnaic materials of CoCr.sub.2 O.sub.7, K and K.sub.2 SO.sub.3 have a poor durability and the said organic materials could hardly maintain a sufficient solar heat-shielding effect for a long period of time. The reason why these organic materials have a poor durability is because they have a poor adhesiveness to vehicles. In addition, the said inorganic materials do not have a sufficient solar heat-shielding effect.
Under the situation, the present inventors repeatedly and earnestly studied so as to overcome the above-mentioned problems and, as a result, have found that a paint composition containing a solar heat-shielding pigment, which has a high solar heat radiation reflectivity in the ultraviolet range, and in the near infrared range and which has a grain size of 50 um or less, in a proportion of from 2 to 60% by weight of the solid content has an excellent long-time durability and may additionally be colored in any desired color with no environmetal sanitary problem, and thus have achieved the present invention.
Accordingly, one object of the present invention is to provide a solar heat-shielding paint composition, which coats the outer surface of outdoor structures which are exposed to direct sunlight, such as various land or marine structures, ships, buildings, household electric appliances and the like thereby to prevent elevation of the internal temperature of the thus coated structures and to display an extreme effect for economization of energy, for example, by reducing the air-conditioning costs, and additionally to lower reduction and vapourization of the content in petroleum tanks or the like.
Another object of the present invention is to provide a solar heat-shielding paint composition which has an excellent long-time durability with no environmental sanitary problem and which can be colored in any desired color to give a beautiful outward appearance.
Still another object of the present invention is to provide a solar heat-shielding paint-coated structure for outdoor use which has an outermost overcoat layer at least made of the said solar heat-shielding paint composition, the said overcoat paint having the function of preventing elevation of the internal temperature in the inside of the thus coated structure thereby to display an excellent effect for economization of energy, for example, by reducing the air-conditioning costs and for prevention of reduction and vapourization of the content in petroleum tanks or the like.
A further object of the present invention is which are provide a solar heat-shielding paint-coated structure which has an outermost overcoat layer at least made of the said solar heat-shielding paint composition and which has an excellent long-time durability with no environmental sanitary problem and can be colored in any desired color to give a beautiful outward appearance.
A still further object of the present invention is to provide a solar heat-shielding paint-coated structure which has an outermost overcoat layer made of the said solar heat-shielding paint composition and additionally has a substrate layer with excellent heat-insulating property, adhesion strength and corrosion-resistance and which has an excellent solar heat-shielding effect, when used under the condition of direct sunlight exposure, and additionally has an excellent long-time durability with no environmental sanitary problem and can be colored in any desired color to give a beautiful outward appearance.